Which of the following muscle groups work both eccentrically and concentrically in the sagittal plane during a squat?

During a squat, the quadriceps are actively involved in both the eccentric and concentric phases of the movement, making them the correct choice for this question.

In the eccentric phase of a squat, which occurs when lowering the body from a standing position into the squat, the quadriceps lengthen as they control the descent against gravity. This action helps to stabilize the knee joint and manage the load being placed on the body.

In the concentric phase, when rising back up from the squat position, the quadriceps contract to extend the knee and lift the body back to a standing position. This dual involvement—lengthening during the descent and shortening during the ascent—exemplifies how the quadriceps function effectively in both directions of the movement in the sagittal plane.

Other muscle groups such as the hamstrings, glutes, and calves have important roles in a squat, but they do not contribute as prominently in both phases as the quadriceps do. For instance, while the hamstrings assist in stabilizing the knee and help with hip extension, their primary action is not as pronounced in the concentric contraction compared to the quadriceps. The glutes also work importantly but are primarily engaged in hip extension rather than the knee flexion-extension sequence